Embodiments of the present invention are directed to integrated circuits and their processing for the manufacture of semiconductor devices. More particularly, embodiments of the invention provide methods and structures for electrostatic discharge (ESD) protection. Merely by way of example, an embodiment has been applied to the manufacture of high frequency input/output of integrated circuit devices, but it would be recognized that the invention has a much broader range of applicability.
Integrated circuits have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Conventional integrated circuits provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of integrated circuits.
Increasing circuit density has not only improved the complexity and performance of integrated circuits but has also provided lower cost parts to the consumer. An integrated circuit or chip fabrication facility can cost hundreds of millions, or even billions, of U.S. dollars. Each fabrication facility will have a certain throughput of wafers, and each wafer will have a certain number of integrated circuits on it. Therefore, by making the individual devices of an integrated circuit smaller, more devices may be fabricated on each wafer, thus increasing the output of the fabrication facility. Making devices smaller is very challenging, as each process used in integrated fabrication has a limit. That is to say, a given process typically only works down to a certain feature size, and then either the process or the device layout needs to be changed. Additionally, as devices require faster and faster designs, process limitations exist with certain conventional processes and materials.
For example, as device size becomes smaller, devices are typically more susceptible to harmful electrostatic discharges. Thus, conventional ESD protection circuits are employed to divert power surges away from susceptible devices to ground. However, with high signal frequencies of input/output interconnects, signal integrity cannot be preserved if the capacitance of an ESD protective device is too high. These and other limitations may be found throughout the present specification and more particularly below.
From the above, it is seen that an improved technique for ESD protection is desired.